Time interval analyzer

ABSTRACT

In an analyzer for time intervals which are defined by two successive electrical pulses each appearing in a separate channel, a first generator delivers recurrent rectangular signals having a period T1 and is triggered by the first pulse, a second generator delivers recurrent rectangular signals having a period T2 of slightly smaller value than the period T1 and is triggered by the second pulse, the signals emitted by each generator being of opposite polarity. Means are provided for detecting the phase reversal of the leading edges of said signals, and a counter which is driven by one of said generators is stopped by said means when a phase reversal of the leading edges has been detected.

United States Patent 91 Barrot et al.

[54] TIME INTERVAL ANALYZER [75] Inventors: Jean-Pierre Barrot, Chemin de la Bouhume; Jacques Negrou; Charles Pelte, both of Les Chenes, all of France [73] Assignee: Commissariat A LEnergie Atomique,

Paris, France [22] Filed: Mar. 2, 1971 [21 Appl. No.: 120,160

[30] Foreign Application Priority Data [4 1 Apr. 3, 1973 [57] ABSTRACT In an analyzer for time intervals which are defined by two successive electrical pulses each appearing in a separate channel, a first generator delivers recurrent rectangular signals having a period T1 and is triggered by the first pulse, a second generator delivers recurrent rectangular signals having a period T2 of slightly smaller value than the period T1 and is triggered by the second pulse, the signals emitted by each generator being of opposite polarity. Means are provided for detecting the phase reversal of the leading edges of said signals, and a counter which is driven by one of said generators is stopped by said means when a phase reversal of the leading edges has been detected.

1 Claim, 2 Drawing Figures COUNTER Spann et a1. ..331/108 D PATENTEUAPR3 197s /COU NTER FIG. 1

FIG. 2

TIME INTERVAL ANALYZER circuit with a pulse regenerator. The line which carries the pulse emitted at the instant 22 is shorter than the line which carries the pulse emitted at the instant t1 so that the second pulse comes progressively closer to the first pulse. When the regenerated pulses are exactly in phase, a coincidence circuit stops the regenerators. This takes place after the second pulse has passed through the circuit a number of times which is proportional to the time interval t2 t1 to be measured; this number is recorded in a suitable device.

Although this method is based on the detection of coincidence of small-width pulses, these pulses must nevertheless be of sufficient width to ensure detection of coincidence in a wholly reliable manner, with the result that coincidence is liable to occur between the rear portion of one pulse and the front portion of the next. Moreover, the trailing edge of the leading pulse has an active function and its time-variation is not necessarily the same as that of the leading edge of the delayed pulse. The accuracy of this method is thus limited by the variations in width and in shape of the leading pulse since it is impossible to compensate for such variations.

This invention proposes a time interval analyzer which also utilizes the transfer of data associated with the instants t1 and :2 within two loop circuits having closely related transit times but which is not subject to the disadvantages attached to the method referred-to above. Said analyzer for time intervals which are indicated by two successive electrical pulses each appearing in a separate channel is primarily characterized in that it comprises a first generator which delivers recurrent rectangular signals having a period T1 and which is triggered by the first pulse; a second generator which delivers recurrent rectangular signals having a period T2 of slightly smaller value than the period T1 and which is triggered by the second pulse, the signals emitted by each generator being of opposite polarity, means for detecting the phase reversal of the leading edges of said signals, and a counter driven by one of said generators and stopped by said means when a phase reversal of the leading edges has been detected.

Further properties and advantages of this invention will become apparent from the following description in which one embodiment of said analyzer is given by way of explanation but not in any limiting sense, reference being made to the accompanying drawings, in which:

FIG. 1 is the general circuit diagram of a time interval analyzer in accordance with the invention;

FIG. 2 represents the operating diagram of said analyzer.

The analyzer which is shown diagrammatically in FIG. 1 is intended to carry out the measurement of time intervals t2 t1 as indicated by two calibrated voltage steps E1 and E2 which are respectively negative and emitted at the instant t1 and positive and emitted at the instant :2. The analyzer is constituted by the following elements:

A first generator 3 which delivers recurrent rectangular electric signals having negative polarity and a period T1 and which is triggered by the voltage step E1;

A second generator 4 which delivers recurrent rectangular electric signals having positive polarity and a period T2 and which is triggered by the voltage step E2; the period T2 is very slightly shorter than the period Tl;

A differentiation capacitor 5 for transforming the rectangular signals derived from the generator 4 into small-width pulses which are alternately positive and negative; the positive pulses correspond to the leading edges of said signals;

A detector circuit so designed that the rectangular signals having a period T1 and the smalLwidth pulses having a period T2 are superimposed at the input of said circuit and that this latter changes state when their sum attains a threshold value; this takes place at an instant at which the phase reversal of the leading edges of both types of rectangular signals has just taken place or in other words when, for the first time, the leading edge of a signal having a period T2 is in advance with respect to the leading edge of a signal having a period T1; this operation naturally entails compliance with the condit1on:

wherein (t2 t1) represents the maximum value of the time intervals to be measured and 1' represents the width of the small-width pulses having a period T2; it is therefore the time interval to be measured which determines the choice of the value assigned to T1;

A counter 7 which is triggered by the generator 4 and stopped by the circuit 6 when the phase-reversal detection has been achieved.

The generator 3 which delivers negative rectangular signals having a period T1 is constituted by a line oscillator of the quarter-wave type, the two main elements of which are a tunnel diode 8 and a short-circuited coaxial line 9 having a length L1 which is proportional to T2/4. The anode of the tunnel diode 8 is grounded whilst the cathode is connected on the one hand to the central conductor of the line 9 through a resistor 10 and on the other hand to a negative-bias voltage source (not shown) through a variable resistor 11. The input to which the voltage step E1 is applied is grounded through a resistor 12 and connected to the cathode of the diode 8 through a resistor 13. The output of said oscillator is coupled to the input of the detector circuit 6 by means of a resistor 14.

The generator 4 which delivers positive rectangular signals having a period T2 is also constituted by a line oscillator of the quarter-wave type having a configuration which is strictly identical with that of the generator 3. The two main components of said generator 4 are a tunnel diode 15 and a short-circuited coaxial line 16 having a length L2 which is proportional to T2/4. The cathode of the tunnel diode 15 is grounded whilst the anode is connected on the one hand to the central conductor of the line 16 through a resistor 17 and on the other hand through a variable resistor 18 to a positivebias voltage source which has not been illustrated. The input to which the voltage step E2 is applied is connected to ground through a resistor 19 and to the anode of the diode through a resistor 20. A resistor 21 serves to couple the output of said generator to the input of the detector circuit 6 through the differentiation capacitor 5.

The essential element of the threshold detector circuit 6 is a tunnel diode 22 whose cathode is grounded and whose anode is connected on the one hand to a positive-bias voltage source (not shown) through a resistor 23 and on the other hand to ground through a rethrough a resistor 26. Stopping of the scaler is effected by a signal which is collected at the anode of the tunnel diode 22 and transmitted through a resistor 27.

The analyzer as herein described operates as follows. The voltage step El (as shown in FIG. 2a) triggers at the instant t1 the first oscillator 3 which delivers to the detector circuit 6 a train of rectangular signals having negative polarity and a period T1 (asshown in FIG. 2b). The voltage step E2 (shown in FIG. 20) then triggers at the instant t2 the second oscillator 4 which delivers a train of rectangular signals having positive polarity and a period T2 (as shown in FIG. 2d) which are counted in the counter 7 and transformed by the capacitor 5 into alternately positive and negative smallwidth pulses (as shown in FIG. 2e).

Since the generator 4 is triggered at an instant t2 such as to ensure compliance with the condition the leading edges of the negative signals having a period Tl first precede the leading edges of the positive signals having a period T2 but this lead decreases progressively and a phase reversal of said leading edges accordingly takes place. When the leading edge of a signal having a period T2 leads for the first time with respect to the leading edge of a signal having a period Tl, a positive small-width pulse is superimposed at the input of the detector 6 on the zero-level portion which separates two rectangular signals (as shown in FIG. 2]). The tunnel diode 22 then changes state and interrupts the counting by the counter 7 of the signals delivered by the generator 4. The reversal of state occurs at an instant 13 at which said scaler indicates a number N such that This number which can be either displayed on luminous tubes or recorded by means of a printer accordingly makes it possible to obtain the value of the time interval t2 1 with an absolute error which is equal to the difference between the periods of the two oscillators.

Thus, whereas the time interval to be measured determines the choice of the value of T1, it is the desired degree of precision which governs the difference T1 T2. Accuracy to within less than l0 picoseconds can be achieved with operating frequen cies in the vicinity of 25 Mc/s.

It is very readily apparent that the analyzer in accordance with the invention has an accuracy of measurement which is distinctly superior to that of devices which detect the coincidence of small-width pulses and the accuracy of which is primarily limited by the variation in width of said pulses. In fact, only the variation in the difference in period Tl T2 limits its accuracy. However, since both oscillators are identical and have very similar periods, they drift in the same manner and the difference T1 T2 is practically not subject to variationfMoreover, said analyzer is of very simple design and only has three active components; only two adjustments are required (resistors 11 and 18) and are particularly rapid.

This invention is not limited solely to the embodiment which has been described with reference to the drawings and which has been given only by way of example. In particular, any other type of oscillator can undoubtedly be employed and especially half-wave oscillators of the type which can be obtained by terminating a single-unit integrated ECL gate by means of a coaxial line. Moreover, the scaler can be driven indifferently by either of the two oscillators. Finally, the drawings do not show the auxiliary circuits which are located upstream of the inputs E1 and E2 and serve to adaptthe device to the measurementof a time interval which is defined by two pulses having any shape and level. I

What we claim is:

1. A time interval analyzer for time intervals indicated by a first and a second electrical pulse in succession, comprising a first generator which delivers recurrent rectangular signals having a period T1 and which is triggered-by said first pulse, a second generator which delivers recurrent rectangular signals having a period T2 of slightly smaller value than the period T1 and which is triggered by said second pulse, the signals emitted by each generator being of opposite polarity, means for detecting the phase reversal of the leading edges of said signals, and a counter driven by one of said generators and stopped by said means when a phase reversal of the leading edges has been detected, said means for detecting the phase reversal of the leading edges of the rectangular signals emitted by the two generators including a capacitor for transforming the rectangular signals having a period T2 into alternately positive and negative small-width pulses and a tunnel diode to which the rectangular signals having a period T1 and said small-width pulses are applied. 

1. A time interval analyzer for time intervals indicated by a first and a second electrical pulse in succession, comprising a first generator which delivers recurrent rectangular signals having a period T1 and which is triggered by said first pulse, a second generator which delivers recurrent rectangular signals having a period T2 of slightly smaller value than the period T1 and which is triggered by said second pulse, the signals emitted by each generator being of opposite polarity, means for detecting the phase reversal of the leading edges of said signals, and a counter driven by one of said generators and stopped by said means when a phase reversal of the leading edges has been detected, said means for detecting the phase reversal of the leading edges of the rectangular signals emitted by the two generators including a capacitor for transforming the rectangular signals having a period T2 into alternately positive and negative small-width pulses and a tunnel diode to which the rectangular signals having a period T1 and said small-width pulses are applied. 